Abstract: In order to explore the influence of water content and the sterilized soil on the root architecture and rhizosheath formation of Kengyilia hirsuta at the seedling stage, five water supply levels (10%, 20%, 30%, 40% and 50% of field water capacity) were watered in sterilized and unsterilized soil to cultivate K. hirsuta. Several parameters for root architecture and rhizosheath weight were measured under different treatment conditions. The experimental results turn as follows. 1) The symbiotic relationship between K. hirsuta root system and soil microorganisms was found and the high water supply levels significantly increased root crossing numbers and branch numbers in the unsterilized soil (P<0.05). However, the symbiotic relationship was destroyed in the sterilization soil. The total root volume between levels of 40%-50%, the root average diameter under levels of 40%, the branch numbers under levels of 20% and 50%, the number of links and the number of root tips under the water levels of 20%-50%, the total root surface area under the water level of 50% were significantly higher than under 10% level in the sterilization soil (P<0.05). After soil sterilization the microbial community changed and the root morphology index significantly increased compared under the condition of unsterilized soil, such as the total root length and root branch in the 20% level, the number of links and the number of root tips in 20%, 30%, 40% and 50% levels, the total root surface area, the root diameter in the 40% level and the total root volume between in 40% and 50% levels, all differed. 2) Under the different water and soil treatment, the topological index of the root of K. hirsuta at the seedling stage was close to 1. The root branching pattern was close to fishtail branching, which is more suitable to grow in the poor soil. The root architecture of K. hirsuta was optimum in the 20% and 30% levels where the topological index (q_b) and fractal dimension (FD) were significantly higher than other water levels (P<0.05). The function of root system in soil was affected by the difference of biomass distribution between primary root and secondary root, and the elongation and extension ability of roots in the soil (total root length, total root surface area, number of links and number of branches) affected more root architecture than the fixed permeability (root average diameter). 3) There was no interaction effect on rhizosheath formation between the water supply and soil treatment (P>0.05), the factors with different influence degrees to the formation of rhizosheath of K. hirsuta at the seedling stage: water>soil>FD>q_b> fixed permeability. With the increase of water supply levels, the rhizosheath weight increased first and then decreased. The rhizosheath weight was maximum in the unsterilized soil of 20% and 30% field water capacity and in the sterilized soil of 30% field water capacity. q_b, FD and the fixed permeability have significantly positive effects on rhizosheath formation (P<0.05).

Key words: Kengyilia hirsuta, seedling stage, root configuration, rhizosheath